Basic knowledge about Wuchereria bancrofti, the cause of Bancroftian filariasis, is meager due to its apparent occurrence in nature only in man. Much of our knowledge on the behavior of this and other lymphatic-dwelling filarial worms in the definitive host has been obtained from studies on closely related species of the genus Brugia which can infect a variety of mammalian hosts. In the present project work will continue on attempting to establish the subperiodic strain of W. bancrofti in monkey and rodent hosts. Various species of the genus Macaca will be infected and the development of W. bancrofti, collected at various times following inoculation, will be evaluated. Hamsters, multimammate rats and jirds (Meriones unquiculatus) will also be infected and the developmental behavior of the parasite will be described. Further aspects of the Brugia-jird system to be examined include: (1) study of the cell mediated immunity response of cells from various lymphoid organs to various mitogens and whole worm antigens prepared from microfilariae, infective-stage larvae and adult worms; (2) continuation of morphological studies of adult and larval filariae by the electron microscope, and (3) light and electron microscopic studies on arterial and granulomatous inflammation caused by various species of Brugia.